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The only H-M engines that had any H-M markings were those that were modified for customers or were race engines for any type of motorsports. The markings were often "H-M----- the 5 or 6 digits were the RO number that specified the specifications the engine was built to. These numbers were often stamped into a pad at the base of the cylinder head on the block. I'm sure these files are long gone by now. Also, not all of the engines had the letters H-M in the number sequence. Nearly all of the engines supplied to the marine industry went through H-M to my knowledge. Chris-Craft and other large boat buildrs used pairs of 300 or 400 hp engines with one being opposite rotation, Nearly all of the Off Shore racers and boat builders used either H-M 427s or Chrysler 426 hemis. Donzi used mostly 289s of the 225 hp or 271 hp varity but they also used the 221,260 and a few had the 351s in late 1968. Donzi made at least 1 boat for H-Ms atty. in Miami that was called the Donzi Peanut a 14 footer that had a mildly nodified 351 Windsor, at that time nobody knew what the Cleveland or Boss engines looked like.
The only time H-M got involved with the installation was when there was a serious problem with an engine or it was removed for modification or the purchase of a race engine and install. Usually any warrantee problem was handled by the builder/seller of the boat and the engine warrantee was handled much like an auto's would be handled.
When H-M closed the race shop in Miami I got the files of all the owners of engines that were built with a balance job. This included all of the 427 FEs and the small blocks. For a while I was buying up all the 427s I could find when the owners decided to repower their boat. I had enough parts to build 25+ Hi Riser and TunnelPort engines and 8 427 SOHCs. That is a MOTOR!
